Apparatus for foaming a slurry

ABSTRACT

An apparatus is described for foaming a slurry made of sand, water and a hydraulic binding medium by adding a foaming agent with a cylindrical vessel ( 2 ) for receiving the slurry and an agitator ( 7 ) revolving relative to the vessel about the vessel axis. In order to provide simple constructional conditions it is proposed that the agitator ( 7 ) comprises agitating units ( 10 ) distributed over the cross section of the vessel, which agitating units each consist of a rotor parallel to the vessel axis with agitator rods ( 14 ) between retainers ( 12, 13 ) on the face side, which rods are distributed over the circumference, are parallel to the axis and can be driven in an alternating manner in opposite directions.

FIELD OF THE INVENTION

The invention relates to an apparatus for foaming a slurry made of sand,water and a hydraulic binding medium by adding a foaming agent with acylindrical vessel for receiving the slurry and an agitator revolvingrelative to the vessel about the vessel axis.

DESCRIPTION OF THE PRIOR ART

In the production of insulating materials and aggregates for theconstruction industry from sands bound with hydraulic binding mediums,e.g. quartz sand or sand-lime, a slurry is formed from the sands, thehydraulic binding agent and the water, which is foamed prior tohardening. It is known for this purpose to add an aluminum powder as anexpanding agent to the slurry, which powder splits the water intohydrogen and oxygen and thus provides propellants leading to theformation of pores in the slurry. The hardening of the foamed slurryoccurs under the influence of heat and pressure in autoclaves. Thedisadvantageous effect in this known production of such porous buildingmaterials and aggregates is, apart from the comparatively highproduction effort, that the size of the forming pores can hardly becontrolled and it is only possible to take an influence on the poredistribution within the foaming slurry with difficulty.

Tests to avoid these difficulties by mechanical foaming of the slurry byadding a foaming agent such as ionogenic tensides have shown suchslurries can only be foamed insufficiently with conventional agitators.It was only managed to achieve half of a desired minimum porosity of 80percent by volume.

SUMMARY OF THE INVENTION

The invention is thus based on the object of providing an apparatus forfoaming a slurry made of sand, water and a hydraulic binding medium bythe addition of a foaming agent of the kind mentioned above in such away that an even foaming of the slurry with a minimum pore share of 80percent by volume can be ensured.

This object is achieved by the present invention in such a way that theagitator comprises agitating units distributed over the cross section ofthe vessel, which agitating units each consist of a rotor parallel tothe vessel axis with agitator rods between retainers on the face side,which rods are distributed over the circumference, are parallel to theaxis and can be driven in an alternating manner in opposite directions.

By providing agitating units with agitator rods which are parallel totheir rotational axis it is possible to advantageously introduce airinto the slurry. The diameter of the agitator rods determines the sizeof the introduced air bubbles and thus the later pores. The later poresize can be predetermined by the diameter of the employed agitator rods,with thinner agitator rods leading to finer air bubbles and largeragitator rods leading to larger air bubbles. The rotational speed of theagitator rods of the individual agitating units has a direct influenceon the rate of the air introduced into the slurry and thus on the shareof pores. Since the agitating units of the agitator are driven inopposite directions, a conveying effect on the slurry to be foamedoccurs between adjacent agitating units. The slurry is sucked in on theside of rods of adjacent rotors rotating into the interstitial regionand is ejected on the opposite side of the interstitial region. Thisconveying effect ensures in combination with the relative rotationbetween the entire agitator and the vessel an even inclusion of theentire slurry mass and thus an even distribution of pores over thefoamed slurry. When making a respective choice of the rotational speedof the agitator rods, air can be introduced in a quantity which makes upat least 80 percent by volume of the foamed slurry even in the case ofslurries whose shares of solids have a higher density than water; thisoccurs under an even distribution of the air bubbles whose size dependssubstantially on the diameter of the employed agitator rods. The foamstructure of the foamed slurry is surprisingly sufficiently stable untilthe setting of the hydraulic binding medium within the slurry prevents acollapse of the foam, namely under the usual ambient conditions withoutthe addition of any additional thermal energy, which may be supplied inany case however to accelerate the setting. In order to enable drivingthe rotors of the individual agitating units in an alternating manner inopposite directions, the rotors can comprise drive shafts which areoperatively connected at least in groups by way of mutually combinggearwheels. The mutually combing gearwheels of adjacent rotors ensurethe opposite direction of rotation of adjacent agitating units. The factthat the mutual distance of the agitating units cooperating in pairs ispreferably chosen in a uniform way benefits the drive of the rotors bymutually engaging gearwheels.

In order to provide simple constructional conditions, the retainers forthe agitator rods can sit on the drive shafts of the agitating units.The agitator rods of the agitating units enclose the respective driveshaft in at least one concentric pitch circle. If the agitator rods arearranged in two or more pitch circles then it is recommended to mutuallyoffset the agitator rods of the individual pitch circles to form a gaprelative to the agitator rods of adjacent pitch circles. This allows aneven introduction of the air into the slurry in combination withfavorable conveying conditions for the slurry.

As a result of the conveying effect of the agitating units cooperatingin pairs on the slurry to be foamed, congestion effects can occur in theintake region of two adjacent agitating units, which congestion effectsobstruct the even advance of the slurry between adjacent agitatingunits. To ensure that such congestion effects cannot have adisadvantageous effect on the air introduction into the slurry, therelative direction of rotation between the vessel and the agitator canbe reversed, so that in the case of a repeated reversal of the directionof rotation of the vessel any congestion regions in the intake regionbetween two agitating units are dissolved when an opposite conveyingcomponent acts upon the slurry as a result of the direction of rotationof the vessel contrary to the intake direction. In contrast to areversal of the direction of rotation of the agitating units, a reversalof the movement of the relative rotation between the vessel and theagitator does not disturb the continued even introduction of air intothe slurry.

Since the rate of air introduction changes with the degree of foaming ofthe slurry at the same rotational speed of the agitator rods, theintroduction of air can be controlled depending on the degree of foamingby the rotational speed of the agitator rods, so that the introduced airquantity can be increased, reduced or kept constant with increasingfoaming of the slurry depending on the respective requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is shown in the drawings by way ofexample, wherein:

FIG. 1 shows an apparatus in accordance with the invention for foaming aslurry in a simplified axial sectional view;

FIG. 2 shows this apparatus in a top view;

FIG. 3 shows an agitating unit in an axial sectional view on an enlargedscale, and

FIG. 4 shows said agitating unit in a sectional view along the lineIV-IV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrated apparatus for foaming a slurry comprises a frame 1 inwhich a cylindrical vessel 2 is rotatably held about the vessel axis forreceiving the slurry to be foamed. For this purpose the frame 1 forms acarrying ring 3 into which the vessel 2 is hooked. Track rollers 4 areprovided for supporting the vessel 2 on the carrying ring 3. The vessel2 rests on the same via a boundary flange 5. A device 6 for dischargingthe foamed slurry in the form of a discharge slide is provided in thefloor of the vessel 2.

An agitator 7 is used for foaming the slurry, which agitator is held ina carriage 9 being vertically adjustable on guide pillars 8 and consistsof a plurality of agitating units 10. Said agitating units 10 formrotors which are parallel to the vessel axis and which each consists ofa drive shaft 11 according to FIGS. 3 and 4 on which disk-like retainers12 and 13, between which the axially parallel agitator rods 14 arearranged. Said agitator rods 14 which are preferably formed by wiresstretched between the retainers 12 and 13 are evenly distributed inconcentric pitch circles about the drive shafts 11. Since the air volumeintroduced via these agitating units 10 not only depends on therotational speed of the agitator rods 14 but also on their number, it isrecommended to arrange the agitating rods in at least two concentricpitch circles for higher introduction performance, since the rotationalspeed of the agitating rods is limited as a result of the centrifugalforces acting upon the slurry to be foamed. In the case of anarrangement of agitator rods 14 in two pitch circles, the agitating rods14 of the two pitch circles are offset relative to each other to form agap, as is shown in FIG. 4 in order to ensure an even introduction ofair.

Since the agitating units 10 project with their lower retainers 13 up tothe floor region of the vessel 2, a respective wear and tear of theretainers 13 must be expected. In order to take such wear and tear intoaccount, the lower retainers 13 can be covered with exchangeable wearingplates 15 which are screwed together with the shaft 11 according to FIG.3.

The agitating units 10 are rotatably held in the carriage 9 and carrygearwheels 16 on the ends projecting upwardly beyond the carriage 9. Thearrangement is made in such a way that the gearwheels 16 of adjacentdrive shafts 11 of the agitating units 10 combined into groups comb withone another, so that the agitating units 11 of each group are driven inan alternating manner in opposite directions. The drive per se occursvia a motor 17 which drives the gearwheels 16 of the respectiveinnermost agitating units 10 of the individual group of agitating unitsvia a gearwheel 18 which is coaxial to the vessel axis. It is understoodthat the central gearwheel 18 can also be connected with an agitatingunit 10.

The gearwheels 16 are arranged in an oil-filled gear trough 19 in orderto ensure simple lubrication for the gearwheels 16. The motor 17 issupported on a carrier 20 bridging the gear trough 19.

To ensure that the agitator 7 does not have to be lifted from the vessel2 via the carriage 8 for filling the vessel 2, the carriage 9 ispenetrated by a filling chute 21 which is provided between two groups ofagitating units 10 and projects through the gear trough 19. The slurryto be treated is filled into the vessel 2 through the filling chute 21,which slurry is mixed for example from 170 to 260 kg of a fine-grainedsand meal, 30 to 50 kg of a sand with an average grain size of between70 to 200 μm and a maximum grain size of up to 1 mm and 90 to 150 kg ofcement by adding 120 to 200 L of water. Before a foaming agent is addedto this slurry, a treatment of the slurry with the help of the agitator7 is recommended, which for this purpose is activated during a timeinterval of 1 to 3 minutes for example. The vessel 2 is also made torotate with the activation of the agitator 7, so that a treatment of theslurry can be ensured which is even over the entire volume. Therotational drive of the vessel 2 is carried out by a motor 22 whichdrives a pinion combing a gear rim 23 enclosing the vessel 2 andreversed in its direction of rotation. The actual foaming process occursafter the addition of the foaming agent which consists according to theembodiment of an ionogenic tenside dissolved in a quantity of 2.8 to 4.5L in 110 to 170 L of water. The slurry laced with the hydrous foamingagent is then foamed with the help of the agitator, with the vessel 2reversing its direction of rotation in an alternating fashion. After atreatment period of between 3 and 10 minutes, air is introduced into theslurry and the same is foamed in a fine-pored fashion. For the purposeof stabilizing the foamed slurry, the stirring process can be continuedfor a duration of 2 to 5 minutes, preferably at a lower circumferentialspeed of the agitating units 10. This aftertreatment has the purpose ofimproving the evenness of the pore distribution over the volume of thefoamed slurry. The foamed slurry can then be removed from the vessel 2via the discharge device 6 and can be poured for hardening intotrough-like vats.

As a result of the agitating units 10 rotating in pairs in oppositedirections, a conveying effect is exerted on the slurry to be foamed,which conveying effect draws the slurry into the intake interstitialregion between two adjacent agitating units 10 and ejects the same onthe opposite side. Air is introduced into the slurry in the suction ofthe agitator rods 14 which are driven with a respective rotationalspeed, namely in the form of fine bubbles which determine the fine-poredstructure of the foam. The diameter of the agitator rods 14 determinesthe pore size, so that a certain pore structure can be ensured by thechoice of the thickness of the agitator rods 14. Agitator rods 14 with adiameter of between 1 and 4 mm are usually used depending on the size ofthe pores of the foamed slurry. The rotational speed and the number ofagitator rods 14 influence the introduced air quantity. The rotationalspeed is subject to limits due to the effects of centrifugal force onthe slurry to be foamed so as to avoid driving out air that has alreadybeen introduced. The pitched circle diameters for the agitator rods 14lie in the region of between 20 and 150 mm. The rotational speed of theagitating units 10 is usually 10 to 45 revolutions per second.

1. An apparatus for foaming a slurry of sand, water and a hydraulic binding medium by adding a foaming agent with a cylindrical vessel for receiving the slurry and an agitator (7) comprises agitating units (10) distributed over the cross section of the vessel, which agitating units each consist of a rotor parallel to the vessel axis with agitator rods (14) between retainers (12,13) on the face side, which rods are distributed over the circumference, are parallel to the axis and can be driven in an alternating manner in opposite directions.
 2. An apparatus according to claim 1 wherein, the rotors of the agitator (7) comprise drive shafts (11) which are operatively connected at least in groups by way of mutually combing gearwheels (16).
 3. An apparatus according to claim 1, wherein the retainers (12, 13) for the agitator rods (14) can sit on the drive shafts (11) of the agitating units (10) and that the agitator rods (14) of the agitating units (10) enclose the respective drive shaft (11) in at least one concentric pitch circle.
 4. An apparatus according to claim 3, wherein the agitator rods (14) of the agitating units (10) are mutually arranged in at least two concentric pitch circles in an offset manner to form a gap with respect to the respective drive shaft (11).
 5. An apparatus according to claim 1, wherein the relative direction of rotation between the vessel (2) and the agitator (7) is reversible.
 6. An apparatus according to claim 1, wherein the rotational speed of the agitating units (11) is controllable depending on the degree of foaming. 